Molten metal filtration box heating apparatus

ABSTRACT

A molten metal filtration apparatus is provided. The apparatus includes a filter chamber having a floor, a metal inlet, a metal outlet, and a wall surface adapted to be partitioned by at least one filter element having an open cell structure characterized by a plurality of interconnected voids. The filter element partitions the filter chamber. At least one heater device is provided at an elevation within the filtration chamber that is equal to or below the filter element.

BACKGROUND

This application claims the benefit of U.S. Provisional Application No.62/806,057 filed Feb. 15, 2019, the disclosure of which is hereinincorporated by reference.

The present disclosure relates generally to the field of filteringimpurities from molten metal. In particular, this disclosure relates toa unique design of a molten metal filter box. However, it is to beappreciated that the present exemplary embodiment is also amenable toother similar molten metal filtration systems.

In the melting, refining and forming of metals, especially the castingof molten metals, it is desirable to separate inclusions from the moltenmetal. Such inclusions result from impurities present in the rawmaterials used to form the melt, from slag, dross and oxides which formon the surface of the melt, and from small fragments of the refractorymaterial used to form the chamber or vessel in which the molten metalmelt is formed. Such inclusions, if not removed from the molten state ofthe metal, can result in weakened areas and/or porosity in the finallysolidified metal body—the end product of the casting operation.

Typically, in a metal casting operation, the metal melt is formed andsometimes alloyed or otherwise refined in a furnace wherein theconstituent components are added in the form of unmelted scrap and/orrefined virgin metal. Low density solids tend to migrate to the surfaceof the melt where they either effervesce or float in combination withpartially and completely solidified oxides known variously as slag anddross. These floating impurities can often be scraped from the melt'ssurface. However, higher and similar density impurities tend to remainin some degree of suspension in the liquid melt and cannot be scraped orotherwise visually identified and selectively removed from the moltenmetal.

From a furnace, the molten metal is transferred to a forming step.Transport may be accomplished with a ladle or other device.Alternatively, the molten metal may be drawn directly from the furnaceand flowed through a channeling means to a mold—a process which allowscontinuous casting.

During the transportation or conveyance of the molten metal, it is oftendesirable to ensure that any remaining dross or slag, from the surfaceof the melt, and entrained, exogenous intermetallic inclusions submergedin the melt are removed prior to the final solidification stage.

One method that is used to prevent the inclusion of exogenousintermetallic substances, including slag or dross, in the formed metalbody is to filter the molten metal between the melting furnace and theforming stage. A variety of means for accomplishing this filtration stepare well known to those with skill in the art. Filtering examples can befound in U.S. Pat. Nos. 4,964,993; 4,444,377; 4,426,287; 4,413,813;4,384,888; 4,330,328; 4,330,327; 4,302,502; 4,298,187; 4,258,099;4,179,102; 4,159,104; 4,081371; 4,032,124; 3,869,282; and, 5,126,047,which are herein incorporated by reference.

In such systems, a filter medium or filter element of a temperatureresistant material is used. Preferred materials resist deteriorationfrom melting, chemical reaction with the metal, and erosion at elevatedtemperatures. The filter medium must also maintain structural integrityat elevated temperatures and, of course, must either entrap or preventthe flow of solids and semi-liquids, by chemical reactions and/or bymechanical prevention of their flow therethrough.

Different filter designs are known to those skilled in the art. Forexample, U.S. Pat. No. 5,369,063, herein incorporated by reference,describes a foam filter of alumina which can be formed into a plate.U.S. Pat. No. 5,126,047 teaches a hollow rectangular prism in fluidcommunication with a refractory plate. Cartridge filters comprised ofend plates interconnected by filtration tubes are also used in the art.

Cartridge filters are often considered superior filters because theypossess exceptional throughput, filtration capabilities and longevity.The TKR division of Mitsui Kinzoku introduced a filtering system formolten aluminium called “Metalofilter” in 1972. The Metalofilter isillustrated in FIG. 1. The Metalofilter can be installed after adegassing unit (when provided) and before the casting unit. Inclusionsor impure particles are captured at the surface or in the filter tubesof a cartridge filter. A exemplary cartridge filter is illustrated inFIG. 2. The filter tubes are usually installed in a cartridge with 7,11, 18, 22, or 28 filter tubes.

The TKR Metalofilter includes a heating lid that incorporates a set ofheaters or gas burners to preheat the box and/or maintain molten metaltemperature. The present disclosure provides an improved filter boxwhich provides improved filtering efficiencies.

BRIEF DESCRIPTION

Various details of the present disclosure are hereinafter summarized toprovide a basic understanding. This summary is not an extensive overviewof the disclosure and is neither intended to identify certain elementsof the disclosure, nor to delineate scope thereof. Rather, the primarypurpose of this summary is to present some concepts of the disclosure ina simplified form prior to the more detailed description that ispresented hereinafter.

In accordance with one aspect of the disclosure, a molten metalfiltration apparatus is provided. The apparatus includes a filterchamber having a floor, a metal inlet, a metal outlet, and a wallsurface adapted to be partitioned by at least one filter element havingan open cell structure characterized by a plurality of interconnectedvoids. The filter element partitions the filter chamber. At least oneheater device is provided at an elevation within the filtration chamberthat is equal to or below the filter element.

In accord with a further embodiment, a method of preheating andoperating a molten metal filtration box is provided. The method includesthe step of providing a molten metal filtration apparatus comprising afilter chamber having a floor, a metal inlet, a metal outlet, and a wallsurface adapted to be partitioned by at least one cartridge filter. Thecartridge filter has an open cell structure characterized by a pluralityof interconnected voids. At least a first heater device is provided in alid of the filtration box and at least a second heater device isprovided at an elevation within the filtration chamber that is equal toor below the cartridge filter. The method includes the step of operatingboth heater devices for at least a period of preheating and operatingonly the second heater devices during a casting cycle.

According to another embodiment, a molten metal filtration apparatus isprovided. The apparatus includes a filter chamber having a floor, ametal inlet, a metal outlet, and a wall surface adapted to bepartitioned by a plurality of filter elements. The filter elementscomprise filter tubes dispersed between end plates. The filter tubeshave an open cell structure characterized by a plurality ofinterconnected voids. The filter tubes are disposed in at least two rowsand at least two columns. The rows and columns define an open space withat least one heater device positioned within the open space.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and drawings set forth certain illustrativeimplementations of the disclosure in detail. The illustrated examples,however, are not exhaustive of the many possible embodiments of thedisclosure.

FIG. 1 is a cross-sectioned view of a prior art filter box;

FIG. 2 is perspective view of a prior art cartridge filter;

FIG. 3 is a top plan view (partially in phantom) of a filtrationapparatus in accord with the present disclosure;

FIG. 4 is a cross-sectional view of the apparatus of FIG. 3 taken alongline A-A;

FIG. 5 is a top plan view (partially in phantom) of an alternativefiltration apparatus embodiment in accord with the present disclosure;

FIG. 6 is a cross-sectional view of the apparatus of FIG. 5 taken alongline A-A;

FIG. 7 is a top plan view (partially in phantom) of a furtheralternative filtration apparatus embodiment in accord with the presentdisclosure; and

FIG. 8 is a cross-sectional view of the apparatus of FIG. 2 taken alongline A-A.

DETAILED DESCRIPTION

A more complete understanding of the components, processes andapparatuses disclosed herein can be obtained by reference to theaccompanying drawings. These figures are merely schematicrepresentations based on convenience and the ease of demonstrating thepresent disclosure, and are, therefore, not intended to indicaterelative size and dimensions of the devices or components thereof and/orto define or limit the scope of the exemplary embodiments.

Although specific terms are used in the following description for thesake of clarity, these terms are intended to refer only to theparticular structure of the embodiments selected for illustration in thedrawings, and are not intended to define or limit the scope of thedisclosure. In the drawings and the following description below, it isto be understood that like numeric designations refer to components oflike function.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

As used herein, the terms about, generally and substantially areintended to encompass structural or numerical modifications which do notsignificantly affect the purpose of the element or number modified bysuch term.

As used in the specification and in the claims, the term “comprising”may include the embodiments “consisting of” and “consisting essentiallyof.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,”“contain(s),” and variants thereof, as used herein, are intended to beopen-ended transitional phrases, terms, or words that require thepresence of the named ingredients/steps and permit the presence of otheringredients/steps. However, such description should be construed as alsodescribing compositions or processes as “consisting of” and “consistingessentially of” the enumerated ingredients/steps, which allows thepresence of only the named ingredients/steps, along with any impuritiesthat might result therefrom, and excludes other ingredients/steps.

Referring now to FIG. 2, a representative cartridge filter 12 isdepicted. Plates 14 and 16 receive a plurality of filter tubes 18. Afirst end of the tubes can be open and mate with passages in plate 16while a second end of the tubes can be closed and housed in plate 14(see FIG. 1 illustration). Molten metal flows through the filter tubesand the passages in plate 16 to an outlet of the filter box. Thecartridge filter 12 can be lifted by a forklift or hydraulic positioningequipment, for example, and inserted or removed from a filter box of thetypes illustrated in FIGS. 3-8.

At least portions of the outward facing surface of the open plate 16 canbe covered by a expandable gasket material, for example, Vermiculiteavailable from 3M, which is used to securely seal open plate 16 to thefilter box wall and prevent leakage of molten metal.

The porous, ceramic material of the filter tubes 18 can be refractorybonded silicon carbide available from the Metaullics Systems Division ofPyrotek, Inc. and the material of the plates 14 and 16 can be refractorybonded silicon carbide available from Pyrotek, Inc.

Cartridge filter equipped filtration boxes are most typically used in acontinuous casting process. An exemplary cast operation would processabout 50 metric tons of molten metal at a rate of 1600 lbs/min. Due tothe requirement to reset the casting pit, there can be 60 or more holdsduring a cast operating process (i.e., before the furnace is depletedand recycled to a new molten metal batch).

The filter tubes and the molten metal within the box during a castingcycle hold must be maintained at elevated temperatures. As demonstratedby FIG. 1, heating elements have historically been placed in the lid ofthe filtration box to achieve this result.

The present inventors have discovered this to be problematic withrespect to processing magnesium containing alloys such as 3,000 and5,000 series alloys (particularly 5,000 series). Moreover, the higherthe temperature and the longer the hold time the more MgO_((x)) isformed. These oxides serve to shorten the life of the filter tubes. Forexample, when processing 5,000 series alloys, the life of a cartridgefilter may be shortened to 17 metric tons. The present inventors havediscovered that this problem is exacerbated when the atmosphere abovethe molten metal in the filter box is the hottest zone in the unit as aresult of using lid heaters exclusively.

Another shortcoming of existing filtration soy designs is associatedwith the requirement preheat the filter tubes to effectively process themolten metal. Moreover, the tubes should be at 800° C. or higher tofunction properly. The preheating process can take in excess of 15hours. However, the present inventors have learned that heating of theentire depth of filter tubes using box lid can lead to uneventemperature exposure. Moreover, filter tubes closer to the lid heatingelements will be exposed to a higher temperature than 800° C. (forexample) to allow the lower rows of tubes to achieve 800° C. Exposingthe top rows of tubes to higher heating temperatures can damage theexposed filter tubes. Moreover, overheating can cause binder failureand/or tube defects.

Referring now to FIGS. 3 and 4, a first embodiment of the presentdisclosure is illustrated. Filter box 100 includes cartridge filter 112having end plates 114 and 116 with a plurality of filter tubes 118disposed therebetween in rows and columns. Immersion heaters 120, 122and 124 are provided below cartridge filter 112. Glowbar immersionheaters suitable for use in molten metal are available from TounetsuCo., Ltd. Additional heaters can be located in the filter box lid in thesame manner as illustrated in FIG. 1.

The addition of the immerson heaters below the intended melt lineadvantageously avoids over-heating certain filter tubes duringpre-heating, allows preheating to be performed at a faster pace,provides a more consistent temperature throughout the box when metalfilled, avoids overheating the atmosphere above the molten metal whereunwanted oxides are most likely to form, and saves energy by introducingheat into highly thermally conductive metal rather than a gasatmosphere.

The present design further allows greater flexibility in heatingprofiles. For example, if present, the lid heaters can be used incombination with the heaters below the intended melt line during preheatand/or during a casting cycle hold, but otherwise shut-off. Similarly,it is contemplated that the lid heaters and the heaters below the meltliner will be operated at any point in time of the casting process, butbelow the melt liner heaters can be operated at a higher temperature.

Referring now to FIGS. 5 and 6, a second embodiment of the presentdisclosure is illustrated. Filter box 200 includes cartridge filter 212having end plates 214 and 216 with a plurality of filter tubes 218disposed therebetween in rows and columns. Immersion heaters 220, 222,224 and 226 are provided at the same elevation as cartridge filter 212.Moreover, in this embodiment, the cartridge filter 212 is provided witha tube gap 230 to receive heaters 222 and 224. Heaters 220 and 226 arevertically aligned and positioned perpendicular to heaters 220 and 224in the filter box outlet channel 240. This configuration maximizesavailable space and places the heaters in an effective zone adjacent thecartridge filter and submerged in the molten metal during the castingcycle. Additional heaters can be located in the filter box lid in thesame manner as illustrated in FIG. 1.

Referring now to FIGS. 7 and 8, a third embodiment of the disclosure isillustrated. This configuration is similar to the second embodiment butin this instance the gap 330 between the filter tubes 318 has beennarrowed and immersion heaters 322 and 324 are vertically stacked. Thisdemonstrates that a number of configurations are available to bestposition the heater devices in effective locations in and around thecartridge filter tubes.

While the present disclosure illustrates a filter box including acartridge filter, it is contemplated that the positioning of the heaterelements adjacent and below the filter body may also have advantageoususe with other filter designs such as plate or rectangular prismfilters.

To aid the Patent Office and any readers of this application and anyresulting patent in interpreting the claims appended hereto, applicantsdo not intend any of the appended claims or claim elements to invoke 35U.S.C. 112(f) unless the words “means for” or “step for” are explicitlyused in the particular claim.

The exemplary embodiment has been described with reference to thepreferred embodiments. Obviously, modifications and alterations willoccur to others upon reading and understanding the preceding detaileddescription. It is intended that the exemplary embodiment be construedas including all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

1. A molten metal filtration apparatus comprising a filter chamberhaving a floor, a metal inlet, a metal outlet, and a wall surfaceadapted to be partitioned by at least one filter element, said filterelement having an open cell structure characterized by a plurality ofinterconnected voids, wherein the filter element partitions the filterchamber; and wherein at least one heater device is provided at anelevation within the filtration chamber that is equal to or below thefilter element.
 2. The apparatus of claim 1 further comprising at leasttwo heater devices at elevation equal to or below the filter element. 3.The apparatus of claim 2 further comprising a heater device locatedabove the filter element.
 4. The apparatus of claim 3, wherein thefurther heater device is located in a lid.
 5. The apparatus of claim 2,wherein the heater devices have a longitudinal axis and wherein thelongitudinal axes of the two heater devices are perpendicular.
 6. Theapparatus of claim 2, wherein at least two heater devices are positionedat different elevations.
 7. The apparatus of claim 6, wherein one heaterdevice is positioned below an elevation of the filter element and atleast one heater device is positioned in at least substantially the sameelevation plane as a portion of the filter element.
 8. The apparatus ofclaim 2 being comprised of at least three heater devices.
 9. Theapparatus of claim 1, wherein the filter element comprises a cartridgefilter.
 10. The apparatus of claim 1, wherein at least one heater deviceis located in an outlet channel of the apparatus.
 11. A process forfiltering molten metal which comprises providing the apparatus of claim1 and introducing molten metal to the filter medium.
 12. A method ofpreheating and operating a molten metal filtration box comprisingproviding a molten metal filtration apparatus comprising a filterchamber having a floor, a metal inlet, a metal outlet, a wall surface,and a cartridge filter that partitions the wall surface; wherein atleast one first heater device is provided at an elevation within thefiltration chamber that is equal to or below the cartridge filter and atleast one second heater device is provided in a lid of the box; andwherein both heater elements are active for at least a portion of apreheating step and said at least one first heater device is activeduring at least a portion of a casting cycle.
 13. The method of claim12, wherein the first heater device and the second heater device areseparated simultaneously but at different temperatures.
 14. The methodof claim 12, wherein the second heater device is active during thepre-heating step and during a hold step but operating at a lowertemperature during a casting step.
 15. A molten metal filtrationapparatus comprising a filter chamber having a floor, a metal inlet, ametal outlet, and a wall surface adapted to be partitioned by aplurality of filter elements, said filter elements comprising filtertubes dispersed between end plates, said filter tubes having an opencell structure characterized by a plurality of interconnected voids,wherein the filter elements are oriented parallel and partition thefilter chamber, said filter tubes being disposed in at least two rowsand at least two columns, said rows and columns defining an open space,and wherein at least one heater device is positioned within said openspace.
 16. The apparatus of claim 15, wherein said open space extendsfrom a lid of the apparatus to said floor.
 17. The apparatus of claim15, wherein said heater device comprises an elongated body orientedsubstantially parallel to a longitudinal axes of the filter elements.18. The apparatus of claim 17, comprising at least two heater devicespositioned within said open space.
 19. The apparatus of claim 18,wherein said heater devices are parallel and horizontally aligned. 20.The apparatus of claim 18, wherein said heater devices are parallel andvertically aligned.